1. Field of the Invention
The present invention relates to patient therapy. More specifically, the present invention relates to a system, a trackable assembly, program product, and related methods for monitoring a geometry of a radiation treatment apparatus to verify the origin and directions of a coordinates system used during treatment plan delivery.
2. Description of the Related Art
Radiation therapy can be effective in treating certain types of cancerous tumors, lesions, or other “targets.” A vast majority of such targets can be eradicated completely if a sufficient radiation dose is delivered to the tumor or lesion volume. Complications, however, may result from use of the necessary effective radiation dose, due to damage to healthy tissue which surrounds the target, or to other healthy body organs located close to the target. The goal of various radiation procedures, such as conformal radiation therapy treatment, is to confine the delivered radiation dose to only the target volume defined by the outer surfaces of the target, while minimizing the dose of radiation to surrounding healthy tissue or adjacent healthy organs. If the effective radiation dose is not delivered to the proper location within the patient, serious complications may result.
Radiation therapy treatment typically uses a radiation delivery apparatus or device, such as a linear accelerator or other radiation producing source, to treat the target. For example, the conventional linear accelerator includes a rotating gantry which generally rotates about a horizontal axis and which has a radiation beam source positionable about the patient which can direct a radiation beam toward the target to be treated. The linear accelerator can also include a rotating treatment table which generally rotates about a vertical axis and which can position the target within a rotational plane of the rotating gantry. Various types of apparatus can further conform the shape of the radiation treatment beam to follow the spatial contour of the target as seen by the radiation treatment beam, from a linear accelerator, as it passes through the patient's body into the target during rotation of the radiation beam source. Multileaf collimators having multiple leaf or finger projections can be programmed to move individually into and out of the path of the radiation beam to shape the radiation beam.
Various types of radiation treatment planning systems can create a radiation treatment plan, which, when implemented, will deliver a specified dose of radiation shaped to conform to the target volume, while limiting the radiation dose delivered to sensitive surrounding healthy tissue or adjacent healthy organs or structures. Typically, the patient has the radiation therapy treatment plan prepared, based upon a diagnostic study through the use of computerized tomographic (“CT”) scanning, magnetic resonance (“MR”) imaging, or conventional simulation films, which are plain x-rays generated with the patient, and thus, the patient's tumor or lesion in the position which will be used during the radiation therapy treatment.
Regardless of which radiation generating apparatus or technique is used at the time of the diagnostic study to develop the radiation therapy treatment plan, in the delivery of either conformal radiation therapy treatments or static radiation therapy treatments, etc., the position of the target with respect to the radiation delivery apparatus is very important. Successful radiation therapy depends on accurately placing the radiation beam in the proper position upon the target. Thus, it is necessary to relate the position of the target at the time of the diagnostic study to how the target will be positioned at the time of the radiation therapy treatment. It is also necessary to maintain an alignment between the radiation delivery apparatus and the target throughout the delivery of the radiation therapy. If this positional relationship is not correct, the radiation dose may not be delivered to the correct location within the patient's body, possibly under treating the target tumor or lesion and damaging healthy surrounding tissue and organs.
Placement of the radiation beams in the proper juxtaposition with the patient to be treated can be accomplished by referencing both the radiation beam and the patient position to a coordinate system referred to as the isocenter coordinate system, which is defined by the geometry of the radiation delivery apparatus. In the linear accelerator example, the gantry, the treatment table, and collimator each have axes of rotation designed to intersect at a specific location in the middle of a treatment room, referred to as the isocenter, an origin of an interesting coordinate system of the treatment room, correspondingly referred to as the isocenter coordinate system. The isocenter coordinate system is nominally defined as horizontal (x-axis), vertical (z-axis), and co-linear with the axis of gantry rotation (y-axis). The isocenter of these three axis of interest is determined and used as a reference “point” to orient the target to the radiation treatment plan during treatment plan development and subsequent radiation delivery.
In order to deliver the radiation therapy in accordance with the radiation plan, the position of the patient is adjusted to dispose the target at the isocenter of the linear accelerator. In general, the patient is positioned on the treatment table of the radiation delivery apparatus to conform to the position used during formulation of the treatment plan. The treatment table is further rotated to then dispose the target at the isocenter to align the view of the target with that view expected by the collimator or other radiation delivery apparatus of the linear accelerator, according to the radiation treatment plan. The treatment table is then locked in place, and the patient is immobilized so that the radiation therapy treatment can be started.
Also, in the linear accelerator example, the isocenter of gantry rotation is the point where the radiation beams from the collimator intersect as the gantry of the linear accelerator carrying the radiation beam source rotates around the target in the patient. There are various methodologies of determining the location of this isocenter. For example, one methodology of determining the isocenter of gantry rotation includes attaching to the gantry a marking device, such as a long rod holding a marking implement, positioning a vertically oriented sheet of receiving material, such as paper, adjacent the marking device. The gantry is then rotated to form an arc or a circle on the receiving material. The operator can then examine the arc or circle to determine the origin of the circle, which relates to the isocenter. Also for example, the operator can actually deploy the radiation beam in order to measure the direction of the radiation beam during rotation of the gantry. Other physical measurements can also be taken to help the operator determine an approximate location of the isocenter. For example, described in co-pending application Ser. No. 11/005,643, by Scherch et al., entitled “System for Analyzing the Geometry of a Radiation Treatment Apparatus, Software and Related Methods,” incorporated by reference, is a system, apparatus, software and methods that can measure the rotation of various components of the mechanical system of the radiation treatment apparatus or device to determine the location of the radiation beam and the positioning of the patient in order to precisely define the isocenter coordinate system used by the operator.
Regardless of the methodology used to determine isocenter, once the isocenter coordinate system has been determined, the radiation beam arrangement and patient positioning can be referenced to the isocenter. Lasers, typically mounted on the wall of the treatment room, are then pointed or directed to cross at the isocenter to identify the location of the isocenter.
Recognized by the Applicants, however, is that the above described methodologies of determining isocenter generally do not account for continuing degradation of the gantry during the actual delivery of the radiation treatment. Also, existing systems, which indicate to the operator the position of the isocenter coordinate system, i.e., the above described lasers, are not accessible during the course of the radiation treatment. Therefore, many systems must rely on the accuracy of a calibrated tracking system to reliably indicate the isocenter coordinate system during radiation delivery. Also recognized, however, is that these systems are vulnerable to inadvertent changes in that calibrated position.
Specifically, the “camera” of the optical tracking system is typically structurally removed from the gantry by a great distance and fixedly connected to a wall or ceiling mount. This “rigid mounting” of the camera may actually move around relative to isocenter. Even slight movements in the camera mounting can have a significant effect on the accuracy of the optical tracking system, due to the great distance between itself and the isocenter, and thus, the optical tracking system requires a specific pre-operation “morning” quality assurance examination to determine if any such changes have occurred.
Thus, also recognized by the Applicants is the need for a system, an assembly, program product, and related methods for continuously monitoring a geometry of a treatment apparatus or device during treatment to continuously verify the origin and orientation of a coordinate system used by the tracking system or device to reference the radiation beam and the patient position to accurately place a radiation beam in a proper juxtaposition with the patient being treated.